In surface-enhanced spectroscopy (SES), such as surface-enhanced Raman spectroscopy (SERS), vibrationally excitable levels of an analyte are probed. The energy of a photon can shift by an amount equal to that of the vibrational level excited by the photon (Raman scattering). A Raman spectrum, which consists of a wavelength distribution of bands corresponding to molecular vibrations specific to the analyte being probed, may be detected to identify the analyte. In SERS, the analyte molecules are in close proximity, for instance, less than tens of nanometers, to metal nano-particles that may be or may not be coated with a dielectric, such as silicon dioxide, silicon nitride, and a polymer, that, once excited by light, set up plasmon modes, which create near fields around the metal nano-particles. These fields can couple to analyte molecules in the near field regions. As a result, concentration of the incident light occurs at close vicinity to the nano-particles, enhancing the Raman scattering from the analyte molecules.
SERS has recently been performed to probe materials beneath a surface through insertion of an optical fiber having a hollow core containing metal nanoparticles through the surface. Conventional optical fibers have openings at distal ends of the optical fibers for the material to be collected into the hollow core and onto the metal nanoparticles. SERS is then performed on the collected material through application of excitation light onto the metal nanoparticles and materials and detection of Raman scattered light from the materials.